The lens system of groups of lens elements uses mechanisms such as cam to shift the groups of lens elements independent of one another along the optical axis, thereby attaining zooming and focusing adjustments. In the case of the zoom lens of three groups of lens elements, a cam barrel of synthetic resin is provided with three cam grooves or cam ridges, so as to obtain a zoom lens having improved features of the reduced number of components, a simplified structure, and an ensured operation (see Patent Document 1 listed below).
A prior art zoom lens disclosed in Patent Document 1 includes, as shown in FIGS. 4 and 5, first to third groups of lens elements respectively denoted by reference numerals 110, 112, and 114. The zoom lens includes a first fixed barrel 122, a cam barrel 126 of synthetic resin disposed outside the first fixed barrel, and studs 180 related to the first group of lens elements where the cam barrel 126 is provided with a single type of cam related to the first group of lens elements 110 closest to the object and at least two types of the cam, 162 and 164, related to two or more groups of lens elements including the second group and/or the one(s) behind it, and the studs 180 are fixed to a forward extension of the fixed barrel 122 to scotch the revolving cam barrel 126. The cam barrel 126 slides over the first fixed barrel 122 but is inhibited from moving simply along the optical axis.
This arrangement takes a half measure of notches 200 at the foremost edge of the cam barrel 126 to receive the studs 180 for the incorporation of both the cam barrel 126 and the studs 180, as shown in FIG. 5. Since the studs 180 related to the first group of lens elements are fixed to the first fixed barrel 122 at closer locations to the object, the notches 200 to receive the studs carrying the first group of lens elements are deployed, circumferentially extending in a plane orthogonal to the optical axis.
List of Document Cited Herein    Patent Document 1: Japanese Patent Preliminary Publication No. 2001-91813
The zoom lens disclosed in Patent Document 1 is, as stated above, provided with the notches 200 circumferentially extending in the plane orthogonal to the optical axis, and this restricts a forward dimension and a shape of the foremost edge of the cam barrel 126. Specifically, in the case that there are three of the studs 180 and the cam barrel 126 revolves within a rotation range up to 90-degree angle, there remains a space occupied by three 30-degree revolving cam ranges in the foremost edge extended forwardly from the cam barrel 126. Cams are typically deployed along a spiral line about the optical axis, and the 30-degree revolving ranges are excessively narrow to the cams, or rather, substantially it is impossible to deploy the cams in that forward extension of the cam barrel.
The zoom lens disclosed in Patent Document 1 has disadvantages as mentioned below:
First, since the cams, which are preferably deployed in a spiral line about the optical axis, cannot be accommodated in an excessively narrow deployment within the 30-degree revolving ranges, it is substantially impossible to dispose the cams in the forward extension from the cam barrel, and resultantly, the lens system must be oversized.
Second, a barrel 128 carrying the first group of lens elements is held between the studs 180 and an inner surface of a second fixed barrel 130, and hence, in the event of a wide-end setting where the lens elements of the first group are in positions closest to the object, the studs 180 press down the shuttling barrel 128 against the inner surface of the second fixed barrel 130 at points only a short distance from terminated edges of the barrels, resulting the first group of lens elements in being held unstably.
Third, first linear grooves 182, which are formed in the barrel 128 supporting the first group of lens elements 110, are to be identical in length to a displacement of the first group of lenses 110 along the optical axis, and thus, the lens barrel 128 must have a longitudinal extension sufficiently long, exceeding the displacement of the first group of lens elements 110 along the optical axis. This brings about the disadvantages of preventing the lens system from being downsized, and increasing in costs for the materials and the mold manufacturing.
The present invention is made to overcome the aforementioned disadvantages of the prior art zoom lens, and accordingly, first of all, it is an object of the present invention to provide a lens barrel and a compact lens system incorporating the lens barrel where studs carrying the foremost group of lens elements are movable along the optical axis integratedly with the rearmost group of lens elements and components holding the same, so that notches defined in a cam barrel to serve as bolt holes and disengage the studs are reduced in dimensions both along and around the optical axis, thereby ensuring enlarged cam formation ranges in the cam barrel and resultantly downsizing the lens system as a whole.
It is another or a second object of the present invention to provide a lens barrel and a lens system incorporating the lens barrel where in the event of a wide-angle setting where the lenses of the foremost group are in their respective closest positions to the object, linearly-sliding studs press down a shuttling barrel against an inner surface of a fixed barrel at points sufficiently away from terminated edges of the barrels so as to stably hold the foremost group of lens elements.
It is still another or a third object of the present invention to provide a lens barrel and a lens system incorporating the lens barrel where it is unnecessary to extend linear grooves in a lens barrel related to the foremost group of lens elements in concurrence with an extended displacement of that group of lens elements along the optical axis, and the lens barrel itself can decrease a length along the optical axis. Resultantly, the lens system, as a whole, can be downsized and reduce costs for the materials and the mold manufacturing.